Archive for December, 2015

The Sky This Week, December 29, 2015 – January 2, 2016 !

The Sky This Week, 2015 December 29 – 2016 January 5

Happy New Year!
Orion, Sirius, and the Pleiades
Imaged on New Year’s Eve 2011 – 2012 from Morattico, Virginia

2015 ends with the Moon waning in the early morning sky. First Quarter occurs on January 2nd at 12:30 am Eastern Standard Time. During the early morning hours Luna drifts past the bright planets that are strung out along the Ecliptic. Look for bright Jupiter near the Moon on the morning of the 31st. On the morning of January 3rd Luna forms a nice triangle with ruddy Mars and the bright blue-tinted star Spica. She ends the week closing in on dazzling Venus in the brightening morning twilight.

The latest sunrise of the year occurs on January 5th, when Old Sol crests the horizon at 7:27 am EST here in Washington, DC. On that same evening sunset occurs at 5:00 pm, 14 minutes later than its earliest sunset back on December 7th. The total length of daylight on New Year’s Day will be 9 hours 30 minutes, four minutes longer than it was on the day of the solstice, and the days will steadily increase in length until the summer solstice, which will fall on June 20.

January 2nd marks the date of Earth’s perihelion, its closest distance to the Sun. On this date we’ll be a mere 147 million kilometers (91.4 million miles) from the fierce surface of the “day star”.

New Year’s Eve is perhaps the one night of the year when almost everybody stays up late to send the old year packing and welcome the new. It’s also a great time to go out and look at the stars. Face toward the south and you’ll be presented with the magnificent Great Winter Circle asterism, centered on the bright of the constellation Orion, the Hunter. Draw an imaginary line through Orion’s “belt” stars and extend it to the southeast and you’ll run into Sirius, the brightest star in the entire sky. By a curious coincidence of timing and the 26,000-year precession cycle, Sirius crosses the meridian at local midnight on New Year’s Eve, a fitting astronomical marker for this annual event. Sirius also marked the beginning of the New Year for the ancient Egyptians. In their timekeeping system the new year began with the annual inundation of the Nile River, which usually began in mid to late July. Around 2800 BCE Egyptian astronomers noticed that Sirius rose just before sunrise on July 21, just as the flood was getting underway. Since their civil calendar only had 365 days in it, the annual cycle of heliacal risings of Sirius and soon became out of synch with their civil day-count. However, after 1461 of their calendar years the heliacal rise once again corresponded with the beginning of the civil calendar year. A testament to the duration of the Egyptian civilization is the fact that they observed this coincidence three times during the civilization’s lifetime.

Midnight revelers might notice a bright object cresting the horizon in the east. This is the giant planet Jupiter, gradually making his way into the evening sky. Jupiter lords over the morning sky and is still very well-placed for skywatchers who rise with morning twilight. Old Jove gets a visit from the Moon on the last morning of 2015, offering two great targets for any telescopes that appeared under the Christmas tree.

Ruddy Mars spends the week drifting eastward from the bright star Spica and also gets a visit from the Moon on the morning of the 3rd. Mars is gradually beginning to increase in brightness and in the apparent size of his distant disc. 2016 will be a banner year for observing Mars. When he reaches opposition in late May he’ll be almost as bright as Jupiter.

Venus is now dropping toward the Sun, but she is still easy to find if you have an open eastern horizon. Her dazzling glow is prominent in the southeast as morning twilight gathers, and on very clear mornings you should be able to follow her for a while after the Sun has risen. She will pass close to golden Saturn on the morning of the 9th.


The Sky This Week, December 15 – 22, 2015 !

The Sky This Week, 2015 December 15 – 22

The season’s colorful lights
Cylindrical projection map of Jupiter
compiled from observations made between 2015 December 4 – 8

The Moon spends this week waxing in the evening skies. First Quarter occurs on the 18th at 3:14 pm Eastern Standard Time. Luna adds light to the sparse starfield of the autumnal constellations. The Moon won’t be close to any bright objects until she rises with the bright star Aldebaran on the evening of the 22nd.

The time of sunset is now beginning to slowly trend a bit later on successive nights. Most of us probably won’t notice much of a difference in the time of sunset this week, but by Christmas Day it should become noticeable to anyone with a casual interest in the sky. At that time the Sun will set five minutes later than it does at the beginning of this week. However, the time of the latest sunrise is still moving later each morning, offsetting the later sunset times. The two trends “cross” each other on the date of the winter solstice, which occurs on the 21st at 11:48 pm EST. At that time the center of the Sun’s disc stands directly over the Tropic of Capricorn just west of the western coast of Australia. This will mark the shortest day of the year for residents of the Northern Hemisphere; here in Washington, DC we’ll have 9 hours and 26 minutes between sunrise and sunset.

As the Moon waxes, the few dim constellations of autumn that occupy the early evening sky become even more difficult to see. Capricornus, Aquarius, and Pisces have no stars brighter than third magnitude, and the sprawling pattern of Cetus has a single second magnitude star as its brightest luminary. From urban locations these constellations are virtually invisible under the best of circumstances, so a vast swath of the sky looks essentially empty. However, you don’t have to wait too long for brighter prospects to appear. By 9:00 pm nine of the 25 brightest stars in the sky will have cleared the eastern horizon. Anchored by the familiar outline of Orion, the Hunter, the Great Winter Circle provides a welcome touch of light and color for the longest nights of the year. The last of these stars to clear the horizon is Sirius, the brightest star in the sky. Easily found by extending an imaginary line southeastward from Orion’s famous “Belt Stars”, Sirius flickers through all the colors of the rainbow as its light passes through the denser atmosphere near the horizon. Moving clockwise from Sirius you’ll pass Procyon, Pollux, Castor, Capella, Aldebaran, and wind up at Rigel, Orion’s “knee”. Near the center of the circle is the red-tinted star Betelgeuse, which marks one of Orion’s “shoulders”. By midnight these stars are crossing the meridian, blazing away over the winter landscape, unencumbered by the waxing Moon.

Early risers will find the Great Winter Circle settling below the western horizon, replaced by another rather bland area of the constellations of spring. Normally this wouldn’t be a show worth getting up early for, but this year we have a nice array of bright planets to spice up the view. You’ll find giant Jupiter near the meridian at 6:00 am, very well-placed for telescopic observation. Close to the horizon you’ll see the dazzling planet Venus. Last week Venus was occulted by the waning crescent Moon, but before winking out behind the lunar limb she was easily visible to the naked eye in broad daylight. This isn’t all that unusual; many people have mistaken Venus for a high-flying airplane during the daytime. Even my high-school astronomy teacher, who served as a gunnery officer on a convoy transport in World War II, once tried to shoot it down! Between Venus and Jupiter you’ll find ruddy Mars, easily distinguished by his color. The red planet will pass close to the bright star Spica by the week’s end.

The Sky This Week, December 8 – 15, 2015 !

The Sky This Week, 2015 December 8 – 15

The year’s best meteor shower!
Jupiter with Europa and Io, imaged 2015 DEC 6, 11:39 UT

The Moon leaves the pre-dawn sky and returns in the early evening this week. New Moon occurs on the 11th at 5:29 am Eastern Standard Time. If it’s clear see if you can spot the very thin waning Moon before dawn on the 10th. She should appear in the southeastern evening sky in the fading twilight of the 12th. Over the next few evenings she will move into the sparse starfields of the autumnal sky.

We’re still experiencing the earliest sunsets for the year, but by next week Old Sol begins to slowly take back the night. Sunset on the 15th will occur one minute later than it does on the 8th. The total length of night is still increasing, though, as the Sun has yet to reach his latest rise time. That will occur during the first week of January, when he’ll rise 10 minutes later than he does right now. The longest night of the year will fall on the night of the winter solstice on the 22nd. A detailed account of sunrise/sunset phenomena around the times of the solstices may be found here.

These longest nights of the year offer many treats for the intrepid skywatcher. This week we will be treated to the year’s most consistent annual meteor shower, the Geminids. These tiny bits of cosmic fluff encounter the Earth’s atmosphere for the next couple of weeks, with a peak of activity on the night of December 13/14. If the sky is clear and you find yourself in a dark location away from city lights you can expect to see about 100 “shooting stars” per hour. Even observers in suburban sites can see up to 50 per hour. They appear to emanate from a point in the sky near the stars Castor and Pollux in the constellation of Gemini, the Twins. This “radiant” point is high above the eastern horizon by the late evening, so unlike most of the annual meteor showers they can be seen well before local midnight. Your best view will be between about midnight and 3:00 am, when the radiant is almost straight overhead. The one drawback to the Geminids is that they occur in December, when the idea of lying on your back looking up at the sky doesn’t have quite the same cachet as doing so for the Perseids, which occur in mid-August. Staying warm is the key to enjoying this celestial show, so dress in your warmest clothes and have a Thermos full of your favorite hot beverage handy. The meteoroids originate from an interesting asteroid object known as (3200) Phaethon. In addition to being the first asteroid discovered by a space probe, it passes closer to the Sun than any other named asteroid. It also may be the nucleus of a defunct comet, still sputtering small bits of itself along its orbit which collide with Earth every year in mid-December. Whatever its origin, Phaethon’s dusty wake produces one of the best sky shows you’ll see in the winter sky.

While the morning parade of planets doesn’t benefit from interesting conjunctions with the Moon, the later times of sunrise mean that getting up at 6:00 am will find them in a still-dark sky. You’ll find Jupiter high in the south at this hour approaching the meridian. This is an excellent time to view the giant planet in a telescope through generally steady air, and the bracing chill of the early morning ensures that you’ll be wide awake for the rest of the day. Halfway between Jupiter and the very bright Venus you’ll see the ruddy glimmer of Mars. His disc is still quite tiny in the eyepiece, but moments of steady air will show his bright north polar ice cap. Mars will have a much better showing as we move into spring.

Comet Catalina may be found a few degrees north of Venus for the first few days of the week. I was able to spot it from suburban skies with binoculars over the past weekend. It resembles an out-of-focus greenish star. It will continue to drift northward toward the bright star Arcturus over the course of the rest of the month. This will be its only visit to the inner solar system; its hyperbolic orbit will sent it out to the far reaches of the Oort Cloud next year.

The Sky This Week, December 1 – 8, 2015 !

The Sky This Week, 2015 December 1 – 8

Maidens in chains, flying horses, and a hero with a secret weapon.
Jupiter & Io, imaged 2015 NOV 27, 11:35 UT

This week we find the Moon waning in the pre-dawn sky, wending her way through the rising stars of spring and the bright planets that may be found among them. Last Quarter occurs on the 3rd at 2:40 am Eastern Standard Time. Luna may be found three degrees south of the bright star Regulus on the morning of the 2nd. On the 4th she shares the limelight with bright Jupiter. On the 6th you’ll find the Moon just over four degrees east of ruddy Mars. The finale of this display falls on the morning of the 7th, when the Moon is situated just two degrees east of brilliant Venus. All of these mornings should offer fine photo opportunities for budding astrophotographers.

This week we enter the month-long sequence of sunrise and sunset phenomena that are associated with the Winter Solstice. From now until the 12th we’ll experience the earliest sunsets for the year at mid-northern latitudes. Here in Washington sunset will occur at 4:46 pm EST. After the 12th we begin to get a little of the evening back; by Christmas sunset will occur five minutes later, and by the month’s end the difference will be 10 minutes.

The early evening still hosts the last of summer’s stars with the Summer Triangle hanging above the western horizon. Vega, Deneb, and Altair steadily move lower as the night passes, while to the east the bright stars of the Great Winter Circle make their appearance. In between, few bright stars dominate the sky along the meridian, with the notable exception of yet another geometric figure crossing the mid-point of the sky. The “Great Square” of Pegasus is made up of four second-magnitude stars and dominates an otherwise barren stretch of the heavens. Pegasus represents the famed winged horse from the ancient legend of Perseus and Andromeda, both of whom are located nearby. Andromeda actually shares the northwest corner star of the Square, Alpheratz. You can see two diverging “chains” of stars trending eastward from Alpheratz, one made up of second-magnitude stars and the other composed of fainter third-and fourth-magnitude stars. These represent the chains that bound the beautiful Andromeda to a rock as a punishment for her mother Cassiopeia’s vanity. If you follow the bright chain of stars from Alpheratz you’ll find that it points to the star Mirfak, the brightest star in the constellation of Perseus, the Hero. Perseus resembles a large wishbone to my eye and hosts a number of bright star clusters for owners of binoculars or small telescopes. It’s most famous object is the star that is normally its second-brightest luminary, Algol. This star is the prototype of an “eclipsing binary” variable star. Over the course of just under three days the star’s apparent brightness drops by over a full magnitude and then brightens back to normal, with each eclipse lasting about 10 hours. This “winking” was thought by the ancients to represent the eye of the severed head of the Gorgon Medusa, slain by Perseus in an earlier adventure. In the Andromeda myth Perseus rides to the maiden’s rescue on Pegasus, using the Medusa’s winking eye to turn her tormentor, Cetus the sea-monster, to stone.

It’s well worth your while to rise before the Sun this week as the Moon glides through the bevy of morning planets. Each morning will bring a different configuration for your enjoyment. It is also a great time to get a telescopic view of Jupiter, who is high in the southeast at 6:00 am. The morning sky is usually when we find the least amount of turbulence in Earth’s atmosphere so it’s a great time to look for fine detail on Old Jove’s banded surface. You might also want to catch glimpses of ruddy Mars and dazzling Venus before the Sun crests the horizon.

If you live near a place with a clear view of the eastern horizon and a relatively dark sky, try to track down Comet C/2013 US10 (Catalina). This week it hangs below Venus about 20 degrees above the horizon at around 6:00 am. By the end of the week the comet will be less than five degrees from the dazzling planet and glowing at around 4th-magnitude.